This invention relates generally to apparatus used in conjunction with fire detection and alarm systems. More particularly it is directed to an electro-optic device designed to detect and annunciate the presence of smoke in the air in or moving through the device. To increase the sensitivity of the device to small smoke particles the components of this device are arranged so that both light which is forward scattered and light which is back scattered are efficiently collected.
One of the limitations of optical smoke detectors has been that while they are extremely sensitive to the presence of large smoke particles they have been less sensitive to small smoke particles. By novel structural arrangements in the smoke chamber we have substantially improved the sensitivity of the optical smoke detector to small smoke particles. Small smoke particles are herein defined as those particles having a diameter (D) less than the wavelength of the light being used. The small smoke particles tend to be generated in flash fires or rapidly burning fires in contrast to smouldering fires which tend to result in large smoke particles to be sensed.